os: centos 7.4.1708
db: mysql 8.0.20
版本
# cat /etc/centos-release
CentOS Linux release 7.4.1708 (Core)
#
#
# yum list installed |grep -i mysql80
mysql-community-client.x86_64 8.0.20-1.el7 @mysql80-community
mysql-community-common.x86_64 8.0.20-1.el7 @mysql80-community
mysql-community-devel.x86_64 8.0.20-1.el7 @mysql80-community
mysql-community-libs.x86_64 8.0.20-1.el7 @mysql80-community
mysql-community-libs-compat.x86_64 8.0.20-1.el7 @mysql80-community
mysql-community-server.x86_64 8.0.20-1.el7 @mysql80-community
mysql-community-test.x86_64 8.0.20-1.el7 @mysql80-community
mysql80-community-release.noarch el7-3 installed
# mysql -e "select version();"
+-----------+
| version() |
+-----------+
| 8.0.20 |
+-----------+
innodb_flush_method
lower_case_table_names 默認爲0，當設置爲 1，重啓 mysql 報錯
# mysql
mysql> show global variables like '%innodb_flush_method%';
+---------------------+----------+
| Variable_name | Value |
+---------------------+----------+
| innodb_flush_method | O_DIRECT |
+---------------------+----------+
1 row in set (0.01 sec)
The innodb_flush_method options for Unix-like systems include:
fsync or 0: InnoDB uses the fsync() system call to flush both the data and log files. fsync is the default setting.
O_DSYNC or 1: InnoDB uses O_SYNC to open and flush the log files, and fsync() to flush the data files. InnoDB does not use O_DSYNC directly because there have been problems with it on many varieties of Unix.
littlesync or 2: This option is used for internal performance testing and is currently unsupported. Use at your own risk.
nosync or 3: This option is used for internal performance testing and is currently unsupported. Use at your own risk.
O_DIRECT or 4: InnoDB uses O_DIRECT (or directio() on Solaris) to open the data files, and uses fsync() to flush both the data and log files. This option is available on some GNU/Linux versions, FreeBSD, and Solaris.
O_DIRECT_NO_FSYNC: InnoDB uses O_DIRECT during flushing I/O, but skips the fsync() system call after each write operation.
Prior to MySQL 8.0.14, this setting is not suitable for file systems such as XFS and EXT4, which require an fsync() system call to synchronize file system metadata changes. If you are not sure whether your file system requires an fsync() system call to synchronize file system metadata changes, use O_DIRECT instead.
As of MySQL 8.0.14, fsync() is called after creating a new file, after increasing file size, and after closing a file, to ensure that file system metadata changes are synchronized. The fsync() system call is still skipped after each write operation.
Data loss is possible if redo log files and data files reside on different storage devices, and a crash occurs before data file writes are flushed from a device cache that is not battery-backed. If you use or intend to use different storage devices for redo log files and data files, and your data files reside on a device with a cache that is not battery-backed, use O_DIRECT instead.
參考:
https://dev.mysql.com/doc/refman/8.0/en/innodb-parameters.html#sysvar_innodb_flush_method